DAM/Specific/TBT-DAM-016

Dam Spillway Construction

Dams, Reservoirs & Flood Defence › Specific › Dam Spillway Construction

Presenter		Project
Location		Date

Spillways are channels or structures that safely discharge excess water from reservoirs during flood events.
Construction involves deep excavation, mass concrete placement, and heavy reinforcement fixing.
Spillway works are located near the dam structure, often on steep terrain with water at close proximity.
Rock excavation for spillway channels may require controlled blasting or hydraulic breaking.
Concrete placement in large stepped or sloping channels requires formwork on difficult gradients.
Spillway construction must maintain the dam's flood discharge capacity throughout the works.
Temporary diversion of water flows around the construction zone may be needed during heavy rainfall.
Working near the reservoir edge and within the spillway channel creates constant drowning hazards.
Vibration from blasting and breaking near the dam embankment requires monitoring to prevent damage.
Quality control of the concrete and erosion-resistant finishes is essential for long-term performance.

Flood safety	The spillway must function during construction — any blockage could cause uncontrolled overtopping of the dam.
Drowning risk	Working near and within water channels at the base of a reservoir creates serious and constant drowning hazards.
Structural durability	Spillway concrete must resist extreme water velocities — poor quality leads to erosion and structural failure.

Don't

Maintain the spillway flood discharge capacity throughout the construction programme
Wear personal flotation devices when working near the reservoir edge or in the channel
Install edge protection along the spillway channel walls during construction activities
Monitor vibration from blasting and breaking to protect the dam embankment integrity
Place concrete in accordance with the specification for erosion-resistant finishes
Plan temporary water diversion for the construction zone during heavy rainfall events
Provide safe access to the spillway construction area including stairs and platforms
Brief the team on flood warning procedures and the evacuation route from the spillway
Use formwork designed for the specific gradients and step configurations in the channel
Test concrete quality for every pour to confirm it meets the spillway specification

DON'T block or restrict the spillway discharge capacity during any phase of construction
DON'T work in the spillway channel during heavy rainfall or when reservoir levels are rising
DON'T blast near the dam embankment without vibration monitoring and engineer approval
DON'T access the spillway construction area without a personal flotation device available
DON'T pour concrete that does not meet the erosion resistance specification for the spillway
DON'T leave the spillway channel unprotected with loose materials that could block flow
DON'T ignore weather forecasts — flash flooding can fill the spillway channel rapidly
DON'T work on steep spillway gradients without secure working platforms and fall protection
DON'T store materials in the spillway where they could be washed downstream during a flood
DON'T skip quality testing — spillway concrete failure during a flood is catastrophic

See also: Dam and Reservoir Safety Awareness | Mass Concrete Pours

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